Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methylsubstituents symmetrically placed on the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenzene (hemimellitene). All three compounds have the formula C6H3(CH3)3, which is commonly abbreviated C6H3Me3. Mesitylene is a colourless liquid with sweet aromatic odor. It is a component of coal tar, which is its traditional source. It is a precursor to diverse fine chemicals. The mesityl group (Mes) is a substituent with the formula C6H2Me3 and is found in various other compounds.[3]

Oxidation of mesitylene with nitric acid affords trimesic acid ( C6H3(CO2H)3). Using the milder oxidant manganese dioxide, one obtains 3,5- dimethylbenzaldehyde. With metal centers it functions as a ligand, one example being (η6-C6H3Me3)Mo(CO)3.[4]

Mesitylene is mainly used as a precursor to 2,4,6-trimethylaniline, a precursor to colorants. This derivative is prepared by selective mononitration of mesitylene, avoiding oxidation of the methyl groups.[5]

Mesitylene is used in the laboratory as a specialty solvent. It also serves as a ligand in organometallic chemistry, one example being (η6-C6H3Me3)Mo(CO)3.

In the electronics industry, mesitylene has also been used as a developer for photopatternable silicones due to its solvent properties.

The three aromatic hydrogen atoms of mesitylene are in identical chemical shift environments. Therefore, they only give a single peak near 6.8 ppm in the 1H NMR spectrum. For this reason, mesitylene is sometimes used as an internal standard in NMR samples that contain aromatic protons.[6]

Mesitylene was first prepared in 1837 by Robert Kane, an Irish chemist, by heating acetone with concentrated sulfuric acid.[7] He named his new substance "mesitylene" because the German chemist Carl Reichenbach had named acetone "mesit" (from the Greek μεσίτης, the mediator),[8] and Kane believed that his reaction had dehydrated mesit, converting it to an alkene, "mesitylene".[9] However, Kane's determination of the chemical composition ("empirical formula") of mesitylene was incorrect. The correct empirical formula was provided by August W. von Hofmann in 1849.[10] In 1866 Adolf von Baeyer showed that mesitylene's structure was consistent with that of 1,3,5-trimethylbenzene;[11] however, conclusive proof that mesitylene was identical to 1,3,5-trimethylbenzene was provided by Albert Ladenburg in 1874.[12]

^For an explanation of the original of the name "mesitylene", see also: Henry E. Roscoe, A Treatise on Chemistry (New York, New York: D. Appleton and Co., 1889), vol. III, page 102, footnote 2.

^A.W. Hofmann (1849) "On the composition of mesitilole [mesitylene], and some of its derivatives", The Quarterly Journal of the Chemical Society of London, vol. 2, pages 104–115. (Note: The empirical formula of mesitylene as stated in Hofmann's paper ( C18H12 ) is incorrect; however, this happened because Hofmann used 6 as the atomic weight of carbon, instead of the correct atomic weight of 12. Once the correct atomic weight is used in Hofmann's calculations, his results give the correct empirical formula of C9H12.)